Human endurance stronger at ultra distance

ELIZABETH NORTON

Last updated 20:44 27/06/2013

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The Tor des Geants is considered the world's most challenging footrace.

Consisting of walking and running for about 330 kilometres in the province of Val d'Aoste in the Italian Alps - at an altitude of 2400 metres, a time limit of 150 hours, and no required stops - this ultramarathon gives athletes the ultimate opportunity to test themselves.

It also gives scientists the chance to study the human body when pushed to its limits.

Research just released shows that participants in the Tor show less wear-and-tear than runners in shorter races, suggesting that pacing strategies and possibly fatigue itself may exert a protective effect.

Muscle fatigue and inflammation are common after arduous runs.

For example, when tested for enzymes indicative of muscle and liver damage, runners in the Spartathlon, a continuous 246km race from Athens to Sparta, show the highest levels ever recorded as a result of exercise.

The Tor des Geants, besides being an even longer race, brings in the additional factor of prolonged sleep deprivation.

The route contains refreshment points for food, drink, and rest, but because this time is not deducted from the total, racers sleep as little as possible. (Equipped with headlamps, they continue to run in the dark.)

"Shorter" races are completed by the same elite athletes without stopping to sleep, in 36 hours or less in the case of the Spartathlon.

To explore the effect of extreme conditions and sleep deprivation, sports physiologist Jonas Saugy of the University of Lausanne in Switzerland, and colleagues, tested 15 male runners in the 2011 race before, during, and about 30 minutes after the race.

The researchers used electrical stimulation to test fatigue in the racers' leg and foot muscles; they also took blood samples and asked the participants to rate their feelings of fatigue and pain.

To separate out the sleep deprivation factor, a control group of eight trained runners were limited to a similar amount of sleep (about an hour and a half by the midpoint and about nine hours by the end), but didn't race.

Compared with racers in similar events of one-half to one-quarter of the distance, competitors in the Tor showed less muscle fatigue and much lower levels of inflammation in their blood.

For example, in tests of fatigue in muscles at the knee and foot, racers in the Tor showed only half the decrease in strength observed in runners in the 166km Ultra-Trail du Mont-Blanc, previously studied by the researchers.

Blood levels of creatine kinase, an enzyme released by muscles in response to tissue damage, were much lower than after the Mont-Blanc race, and lower than levels seen in the 161km Western States Endurance Run from Squaw Valley to Auburn, California.

Another biomarker, C-reactive protein, a blood protein that rises in response to inflammation, did increase throughout the Tor, but not to the same extent as in the Mont-Blanc race.

In terms of general fitness, the Tor racers were chosen to be comparable to the Mont-Blanc participants; both groups finished in the top 40 per cent of racers, for example. Sleep-deprived subjects who didn't race didn't show signs of inflammation or muscle fatigue.

Saugy explains that because the race is so very long, competitors were forced to pace themselves and the intensity of exercise was lower overall. Moreover, the sleep deprivation itself exerted a protective effect.

"During the first half of the race, the runners didn't sleep much, about two hours. They tried to run a maximal distance in a minimal time."

In the second part of the race, this sleep deprivation begins to take its toll, Saugy says, and the runners' speeds significantly decrease, preserving the muscle tissue.

In addition, Saugy said, the extra sleep in the second part of the event - forced on the racers by their earlier sleep deprivation - also helped restore the muscles.

"It's good work," said exercise University of California physiologist Martin Hoffman of the study published online in PLOS ONE.

"Field studies of this nature are quite challenging, so just pulling off this study is remarkable," he said.

"It makes perfect sense that the markers of stress and fatigue would be less affected than in shorter events, since the runners would have been exercising at lower intensity to continue for the longer duration."